The present invention is directed to an apparatus for attaching fractured sections of bone in a patient""s body, and is particularly directed to an apparatus that, when implanted, is resistant to toggling in the bone and to being.pulled from the bone. The fixation apparatus prevents relative rotation of the fractured sections of bone without damaging the sections.
Bone screws are used in the medical field for a variety of purposes. Typical uses for bone screws, also referred as anchors, include treating a bone fracture by attaching fractured sections, attaching a corrective device to parts of a fractured bone in an area adjacent to the fracture, and attaching soft tissue, such as a ligament or tendon, to bone.
Most known bone screws use a conventional screw design, i.e. a solid shank, with one or more external thread convolutions. The solid shank and external threads of the conventional bone screws can cause the bone screws to displace and/or destroy an undesirably large amount of bone when implanted. Typically, implantation of a bone screw into bone involves drilling a hole, tapping the hole, and then inserting the screw. In the case of a fracture, such drilling and tapping can further fragment the fractured sections of bone. Such conventional bone screws can also require a large amount of torque to implant the screw into a bone or through a fractured segment of bone. Further, the resistance of the conventional screw to being pulled axially from the bone is dependent upon the surface area of the bone that interfaces with the screw threads.
It is also known to use a corkscrew-style helical spike as a bone screw or tissue anchor. The known corkscrew-style tissue anchors, when implanted, displace less bone than the conventional bone screws, but are generally not able to withstand high tensile loads without structural failure. European Patent No. 0 374 088 A1 discloses a bone screw having a twin-corkscrew design. In this twin-corkscrew design, which is formed by drilling a passage up through a screw having a solid shank and then machining out the material between the two corkscrews, the junction of the corkscrews with the shank is unlikely to be capable of structurally withstanding high tensile loads and repetitive fatigue loads. This structural weakness in the design of the screw in the EP 0 374 088 document is further compounded by the corkscrews having a larger overall diameter than the head of the screw where torque is applied.
Many of the known bone screws, such as those described above, can be susceptible to toggling in the bone and can also pull out of the bone due to the substantial forces on the screws from human body movement and muscle memory. In order to achieve a high pull-out resistance, it is common to use additional screws, which results in an undesirably large amount of bone being displaced. In order to achieve a high pull-out resistance, it is also known to thread a bone screw all of the way through a bone and place a nut on the opposite side. However, use of such a nut increases the complexity of the surgical procedure.
Hence, it is desirable to provide an apparatus for implantation into a bone in a patient""s body in a minimally invasive or endoscopic procedure with a reduced amount of insertion torque required. The desirable apparatus, when implanted, would be highly resistant to toggling in the bone and to being pulled out of the bone despite the substantial forces on the apparatus from human body movement and muscle memory. Further, the desirable apparatus would be able to compress fractured sections of bone together to prevent relative rotation of the fractured sections and permit healing of the fracture without causing any further damage to the fractured sections.
The present invention is an apparatus for attaching a first section of a bone to a second section of the bone. The second section is separated from the first section by a fracture of the bone. The apparatus comprises a bone screw having a platform for drivingly rotating the bone screw and at least two helical spikes for embedding into at least one of the first and second sections of the bone upon rotation of the platform. The at least two helical spikes project tangentially from the platform and extend around a longitudinal axis. The at least two helical spikes have a tip portion at a distal end which penetrates into the bone as the platform is rotated. The bone screw has a first condition in which a first portion of the bone screw extends into one of the first and second sections of the bone. The bone screw further has a second condition in which a second portion of the bone screw extends into the other of the first and second sections of the bone to compress the first and second sections together so that the fracture of the bone can heal. The at least two helical spikes, when embedded into at least one of the first and second sections of the bone, are resistant to toggling in the bone and to being pulled axially from the bone.
In accordance with another feature of the present invention, an apparatus is provided for attaching a first section of a bone to a second section of the bone. The second section is separated from the first section by a fracture of the bone. The apparatus comprises a bone screw for extending between the first and second sections of the bone and for attaching the first section to the second section. The bone screw has a platform for drivingly rotating the bone screw. The bone screw further has at least two helical spikes for embedding into both of the first and second sections of the bone upon rotation of the platform. The at least two helical spikes project tangentially from the platform and extend around a longitudinal axis. The at least two helical spikes have a tip portion at a distal end which penetrates into the bone as the platform is rotated. The bone screw has a first condition in which the at least two helical spikes are embedded into one of the first and second sections of the bone. The bone screw further has a second condition in which the at least two helical spikes are embedded into both of the first and second sections of the bone to compress the first and second sections together so that the fracture of the bone can heal. The bone screw is movable from the first condition to the second condition by rotation of the platform. The at least two helical spikes of the bone screw, when embedded into the first and second sections of the bone, are resistant to toggling in the bone and to being pulled axially from the bone.